Backlight unit and liquid crystal display device comprising the same

ABSTRACT

A backlight unit capable of reducing or effectively preventing a hot spot phenomenon includes a plurality of light sources generating lights, a light guide plate including a portion on which the lights generated from the light sources are incident and converting the lights incident on the portion into a surface-shaped lights and a light path converter converting a traveling direction of the lights incident on the portion of the light guide plate in an area where the lights emitted from the light sources diodes overlap each other.

This application claims priority to Korean Patent application No.2006-0040038 filed on May 3, 2006, and all the benefits accruingtherefrom under 35 U.S.C. §119, the contents of which are hereinincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to backlight units, and more particularly,to a backlight unit for improving light efficiency, and a liquid crystaldisplay device including the backlight unit.

2. Description of the Related Art

A liquid crystal display (“LCD”) device has gradually extended itsapplication range due to light weight, thin thickness, and lowconsumption power driving. The LCD device applies an electric field toliquid crystal materials with dielectric anisotropy, injected betweentwo substrates, and controls the amount of light transmitted into thesubstrates by adjusting the intensity of the electric field, therebydisplaying a desired image.

Since an LCD panel of the LCD device is a non-luminous element thatcannot emit light by itself, the LCD device includes a backlight unitfor providing light to the LCD panel.

A light emitting diode (“LED”) used for the backlight unit has long lifespan, fast lighting speed, low power consumption and high impactresistance, compared to a cold cathode fluorescent lamp (“CCFL”), etc.Moreover, the LED is suitable to make the backlight unit relativelysmall and thin.

Such LEDs are mounted on a light source substrate supplying drivingvoltage to the LEDs. The light source substrate may be bonded to a lightguide plate for guiding an incident light from the LEDs toward an LCDpanel. FIG. 1 is a plan view illustrating a light guide plate and LEDsof a conventional LCD device of the prior art. Maximum light efficiencycan be obtained when emitting surfaces of LEDs 16 are in contact with anincident surface of a light guide plate 24 as illustrated in FIG. 1.However, lights emitted from the LEDs 16 overlap each other in areas “A”where a portion of the light guide plate 24 does not overlap the LEDs16. A “hot spot” phenomenon occurs in that the areas “A”, where thelight emitted from the LEDs 16 overlap each other, include a greateramount of emitting lights than the other areas and thus seem to berelatively bright.

BRIEF SUMMARY OF THE INVENTION

An exemplary embodiment provides a backlight unit capable of reducing oreffectively preventing a hot spot phenomenon and an LCD device includingthe backlight unit.

In an exemplary embodiment there is provided a backlight unit includinga plurality of light sources generating lights, a light guide plateincluding a light incident surface on which the lights generated fromthe light sources are incident and converting line-shaped lightsincident on the portion into a surface-shaped light and a light pathconverter converting a traveling direction of the lights traveling aportion of the light guide plate in an area where the lights emittedfrom the light sources overlap each other.

In an exemplary embodiment there is provided an LCD device including anLCD panel displaying images and a backlight unit supplying lights to theLCD panel. The backlight unit includes a plurality of light sourcesgenerating the lights, a light guide plate including a light incidentsurface on which the lights generated from the light sources areincident and converting the lights incident on the incident surface intoa surface-shaped light and a light path converter converting a travelingdirection of the lights traveling a portion of the light guide plate inan area where the lights emitted from the light sources overlap eachother.

In an exemplary embodiment, the light path converter includes aplurality of dispersion grooves formed from an upper surface and a lowersurface of the portion of the light guide plate.

In an exemplary embodiment, the dispersion grooves are formed along thetraveling direction of the lights and the number of the dispersiongrooves is increased as the dispersion grooves are spaced further awayfrom the light sources.

In an exemplary embodiment, the dispersion grooves form a fan shape ofwhich a width of the fan shape is increased as the dispersion groovesare spaced farther away from the light sources.

In an exemplary embodiment, the dispersion grooves are formed in ahemispheric, semi-circular, or semi-polygonal shape.

In an exemplary embodiment, the light path converter includes aplurality of first dispersion grooves formed at an upper surface of theportion of the light guide plate and a plurality of second dispersiongrooves formed at a lower surface of the portion of the light guideplate.

In an exemplary embodiment, the first and second dispersion grooves faceeach other.

In an exemplary embodiment, the first dispersion grooves are formedbetween the second dispersion grooves.

In an exemplary embodiment, the light path converter disperses theincident lights.

In an exemplary embodiment, the backlight unit further includes a lightscattering part disposed in the dispersion grooves and including ascattering material.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a plan view illustrating a light guide plate and LEDs of aconventional LCD device of the prior art;

FIG. 2 is a perspective view illustrating an exemplary embodiment of anLCD device according to the present invention;

FIG. 3 is a plan view illustrating an exemplary embodiment of a lightincident portion of the light guide plate and the LEDs illustrated inFIG. 2;

FIG. 4 is a perspective view illustrating an exemplary embodiment ofdispersion grooves of the light path converter illustrated in FIG. 3;

FIG. 5 is a view describing an exemplary embodiment of a traveling pathof lights incident into the light path converter illustrated in FIG. 4;

FIGS. 6A to 6D are cross-sectional views illustrating other exemplaryembodiments of dispersion grooves described in FIG. 5; and

FIG. 7 is a cross-sectional view illustrating another exemplaryembodiment of a light guide plate and LEDs according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown. This invention may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, the size and relative sizes of layers and regions may beexaggerated for clarity.

It will be understood that when an element or layer is referred to asbeing “on” or “connected to” another element or layer, the element orlayer can be directly on or connected to another element or layer orintervening elements or layers. In contrast, when an element is referredto as being “directly on” or “directly connected to” another element orlayer, there are no intervening elements or layers present. Like numbersrefer to like elements throughout. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

It will be understood that, although the terms first, second, third,etc., may be used herein to describe various elements, components,regions, layers and/or sections, these elements, components, regions,layers and/or sections should not be limited by these terms. These termsare only used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present invention.

Spatially relative terms, such as “lower”, “under,” “above”, “upper” andthe like, may be used herein for ease of description to describe therelationship of one element or feature to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation, in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “lower” or “under” otherelements or features would then be oriented “upper” or “above” the otherelements or features. Thus, the exemplary term “under” can encompassboth an orientation of above and under. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Embodiments of the invention are described herein with reference tocross-section illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of the invention. Assuch, variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, embodiments of the invention should not be construed aslimited to the particular shapes of regions illustrated herein but areto include deviations in shapes that result, for example, frommanufacturing.

For example, an implanted region illustrated as a rectangle will,typically, have rounded or curved features and/or a gradient of implantconcentration at its edges rather than a binary change from implanted tonon-implanted region. Likewise, a buried region formed by implantationmay result in some implantation in the region between the buried regionand the surface through which the implantation takes place. Thus, theregions illustrated in the figures are schematic in nature and theirshapes are not intended to illustrate the actual shape of a region of adevice and are not intended to limit the scope of the invention.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

The exemplary embodiments of the present invention will now be describedwith reference to the attached drawings.

FIG. 2 is a perspective view illustrating an exemplary embodiment of anLCD device according to the present invention.

Referring to FIG. 2, the LCD device includes an LCD panel 102, abacklight unit supplying light to the LCD panel 102, a mold frame 122 inwhich the LCD panel 102 is positioned, a top chassis 100 encompassingedges of the LCD panel 102 and the mold frame 122, and a bottom chassis108 containing or receiving the backlight unit and its adjacent regiontherein.

The LCD panel 102 includes a first substrate 106, such as a thin filmtransistor (“TFT”) substrate and a second substrate 104, such as a colorfilter substrate that face each other. A sealant (not shown) is disposedbetween the TFT substrate 106 and the color filter substrate 104,essentially bonding the two substrates together. Liquid crystals (notshown) are disposed between the TFT substrate 106 and the color filtersubstrate 104.

The color filter substrate 104 may include a structure in which a colorfilter array, including black matrixes reducing or effectivelypreventing light leakage, color filters representing colors, a commonelectrode forming an electric field perpendicular with a pixelelectrode, and an upper alignment layer coated for the alignment of theliquid crystals on those elements, are formed on an upper substrate.

The TFT substrate 106 may include a structure in which a TFT array,including gate and data lines formed to cross each other, TFTs formed atintersections of the gate and data lines, pixel electrodes connected tothe TFTs, and a lower alignment layer coated for the alignment of theliquid crystals on those elements, are formed on a lower substrate.

The mold frame 122 may include inner sidewalls of a stepped projectionsurface. The backlight unit is mounted on the inner lowermost portion orstep of the mold frame 122, the LCD panel 102 is mounted in the moldframe 122 and optical sheets 136 are mounted between the backlight unitand the LCD panel 102 such that the LCD panel 102 is located on theoptical sheets 136.

The upper chassis 100 is formed substantially in a rectangular band (orframe) shape having plane (e.g. bottom surface) and side surface thatmeet perpendicularly each other. The upper chassis 100 encompasses edgesof the backlight unit and the LCD panel 102 and the mold frame 122. Theupper chassis 100 protects the LCD panel 102 and the backlight unit froman external shock and reduces or effectively prevents a departure ofelements between the upper chassis 100 and the bottom chassis 108 fromeach other.

The bottom chassis 108 supports a light source substrate 118 and LEDs116 mounted on the light source substrate 118 and emits heat generatedand reflected by the light source substrate 118 and a reflection sheet154.

The backlight unit includes a light generator 120, a light guide plate124 to which light is supplied from the light generator 120, a pluralityof optical sheets 136 mounted sequentially on the light guide plate 124and the reflection sheet 154 installed under the light guide plate 124.As illustrated in FIG. 2, the light source substrate 118 may not extendan entire distance of the light guide plate 124 in a transversedirection of the light guide plate 124. In alternative exemplaryembodiments, the light source substrate 118 may extend substantially allof a width of the light guide plate 124 in the transverse direction.

The optical sheets 136 cause light emitted from the light guide plate124 to be incident into the LCD panel 102. The optical sheets 136diffuse the light emitted from the light guide plate 124 and enhanceluminance of the display device. In exemplary embodiments, the opticalsheets 136 may include a diffusion sheet 130, a prism sheet 132 and/or aprotection sheet 134.

The diffusion sheet 130 causes incident light from the light guide plate124 to be directed to the front of the LCD panel 102. Also, thediffusion sheet 130 diffuses the light from the light guide plate tohave uniform distribution over a wide range such that the light can beirradiated to the LCD panel 102. In exemplary embodiments, the diffusionsheet 130 may include a film of a transparent resin of which bothsurfaces are coated with an optical diffusion member. The prism sheet132 converts a traveling angle of light diffused by the diffusion sheet130 into an angle substantially perpendicular to the LCD panel 102. Theefficiency of light is increased when the light incident into the LCDpanel 102 is at right angles with the LCD panel 102 when the prism sheet132 is employed. The protection sheet 134 protects the surface of theprism sheet 132 and diffuses light passing through the prism sheet 132.

The reflection sheet 154 reflects the light incident on itself through arear surface of the light guide plate 124 toward the light guide plate124. In exemplary embodiments, the reflection sheet 154 may include aplate having high light reflectivity, thereby reducing the loss oflight.

The light generator 120 includes the LEDs 116 and the light sourcesubstrate 118 on which the LEDs 116 are mounted.

The LEDs 116 are mounted on the light source substrate 118 and generatelight. The LEDs 116 may be bonded to the light guide plate 124 by any ofa number of methods suitable for the purpose described herein. Lightgenerated from the LEDs 116 are incident on the light guide plate 124through an incident surface formed at one side of the light guide plate124 corresponding to the LEDs 116.

In exemplary embodiments, the light source substrate 118 is formed of aflexible printed circuit (“FPC”) or a printed circuit board (“PCB”). Inone exemplary embodiment, at least two LEDs 116 are mounted on the lightsource substrate 118 such as illustrated in FIG. 2. The light sourcesubstrate 118 emits heat irradiated from the LEDs 116 to the exteriorand supplies a driving voltage to the LEDs 116. In an alternativeexemplary embodiment, more or less that two light sources 116, such asLEDs, may be mounted to the light source substrate 118.

The light guide plate 124 converts a relatively line-shaped lightemitted from the LEDs 116 into a relatively surface-shaped light andguides the surface light source toward the LCD panel 102. The lighttraveling toward the rear surface of the light guide plate 124 isreflected by the reflection sheet 154 and travels toward the light guideplate 124.

A light path converter 110 may be formed in the light guide plate 124 asillustrated in FIG. 3 in an area where a portion of the light guideplate 124 does not overlap the LEDs 116 (or that is between adjacentLEDs 116 in a longitudinal direction of the light guide plate 124) Theportion of the light guide plate 124 that does not overlap the LEDs 116is indicated in an area “B” where lights emitted from the LEDs overlapeach other.

In an exemplary embodiment, the light path converter 110 may be formedof a plurality of dispersion grooves 128. The dispersion grooves 128 maybe formed in a hemispheric, semi-circular and/or polygonal shape asillustrated in FIG. 4. In exemplary embodiments, the dispersion grooves128, such as illustrated in FIG. 4, may include a circular shape on aplane of an upper surface of the light guide plate 124. A profile orcross section of the dispersion grooves 128 taken from the upper surfaceto a lower surface of the light guide plate 124 may be considered tohave a hemispheric, semi-circular and/or polygonal shape.

In one exemplary embodiment, each of the dispersion grooves 128 is about1 to 2 millimeters (mm) in width (taken in a direction substantiallyparallel with a plane of the upper surface of the light guide plate 124)and/or depth (taken in a direction substantially perpendicular to aplane of the upper surface of the light guide plate 124).

As illustrated in FIG. 5, the dispersion grooves 128 are formed along atraveling direction of light (indicated by the dotted line) in an areawhere light emitted from the LEDs overlap each other. As the dispersiongrooves 128 are spaced farther away from the LEDs 116, the number (ordensity) of the dispersion grooves 128 is increased. As illustrated inFIG. 5, the light path converter 110 including the plurality ofdispersion grooves 128 is considered as forming a fan shape of whichwidth of the fan is increased as the dispersion grooves 128 are spacedat a distance farther away from the LEDs 116.

Air is buried or held into the dispersion grooves 128 of the light pathconverter 110. Refractive indexes of the dispersion grooves 128 and thelight guide plate 124 become different. Lights that are incident on thelight guide plate 124 from the LEDs 116 having linearity are refractedand diffracted at a boundary between the light guide plate 124 and thedispersion grooves 128 as illustrated in FIG. 5 by the arrows around thedispersion grooves 128. In one exemplary embodiment, the dispersiongrooves 128 formed in a hemispheric or semi-circular shape include acurvature having different slopes at incident points of lights. Hence,lights incident into the light path converter 110 are refracted indifferent directions according to the incident points of the dispersiongrooves 128 having the curvature. The light path converter 110 includingthe dispersion grooves 128 having curvature to refract incident lightsin different directions can refract lights in various directions whencompared with the light path converter 110 including the dispersiongrooves of a polygonal shape which may have the similar or substantiallythe same slope at incident points.

In the illustrated exemplary embodiments, the light path converter 110is formed on the portion of the light guide plate 124 between the LEDs116 and refracts lights that are incident on the light guide plate 124and that have linearity in various directions. Advantageously, a “hotspot” phenomenon can be reduced or effectively prevented where lightsare concentrated to the portion of the light guide plate 124 between theLEDs 116.

The light path converter 110 may be formed in one of any variety ofshapes, such as shown in FIGS. 6A to 6D. The light path converter 110illustrated in FIG. 6A includes a plurality of dispersion grooves 128formed from the upper surface of the light guide plate 124 in adirection toward the lower surface of the light guide plate 124 at agiven depth. The light path converter 110 illustrated in FIG. 6Bincludes a plurality of dispersion grooves 128 formed from the lowersurface of the light guide plate 124 in a direction toward the uppersurface at a given depth.

The light path converter 110 illustrated in FIG. 6C includes a pluralityof first dispersion grooves 112 formed from the upper surface of thelight guide plate 124 in a direction toward the lower surface of thelight guide plate 124 at a given depth and a plurality of seconddispersion grooves 114 facing the first dispersion grooves 112 andformed from the lower surface of the light guide plate 124 in adirection toward the upper surface at a given depth. The light pathconverter 110 illustrated in FIG. 6D includes a plurality of firstdispersion grooves 112 formed from the upper surface of the light guideplate 124 in a direction toward the lower surface of the light guideplate 124 at a given depth and a plurality of second dispersion grooves114 formed between or alternating with the first dispersion grooves 112and formed from the lower surface of the light guide plate 124 in adirection toward the upper surface at a given depth. In an exemplaryembodiment where the first and second dispersion grooves 112 and 114 areformed at both upper and lower surfaces of the light guide plate 124 asillustrated in FIGS. 6C and 6D, the reduction or prevention of the hotspot phenomenon may be more effective than the case when the dispersiongrooves 128 are formed at one surface of the light guide plate 124 asillustrated in FIGS. 6A and 6B.

Referring to FIG. 7, another exemplary embodiment of the backlight unitaccording to the present invention includes the same elements as shownin FIGS. 2 to 6 except light scattering parts buried in the dispersiongrooves of the light path converter. Therefore, a detailed descriptionof the same elements will be omitted.

Light scattering parts 126 shown in FIG. 7 are formed by burying ordisposing a scattering material in the dispersion grooves 128 of thelight path converter 110. The uppermost surfaces of the light scatteringparts 126 are substantially in parallel with the upper surface of thelight guide plate 124. The light scattering parts 126 scatter refractedlight incident on the light path converter 110, thereby raising adispersion effect of light. Advantageously, the backlight unit canreduce or effectively prevent a hot spot phenomenon that lights areconcentrated to the portion of the light guide plate 124 between theLEDs 116.

As in the illustrated exemplary embodiments, the backlight unit and theLCD device including the same include the light path convertercomprising a plurality of dispersion grooves in an area where lightsemitted from LEDs overlap each other. Then lights having linearityincident on the light guide plate are refracted in various directions bythe light path converter. Advantageously, a hot spot phenomenon thatlights are concentrated to the portion of the light guide plate betweenthe LEDs can be reduced or effectively prevented.

In an exemplary embodiment, since a plurality of dispersion grooves ofthe light path converter may be manufactured by an injection method,additional cost is not required.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1.-19. (canceled)
 20. A method of guiding lights using a light guideplate provided with a light path converter, the method comprising:receiving lights emitted from a plurality of light sources spaced apartfrom each other; and refracting a portion of the lights using the lightpath converter, the portion of the lights being incident into the lightguide plate corresponding to spacing between the light sources.
 21. Themethod of claim 20, wherein the light guide plate comprises a lightincident surface on which the lights are incident, and a portion of thelight path converter adjacent to the light incident surface is disposedonly between adjacent light sources.
 22. The method of claim 21, whereinthe light path converter disperses the lights traveling into the lightguide plate.
 23. The method of claim 20, wherein the light sources arelight emitting diodes.
 24. The method of claim 20, wherein light pathconverter comprises a plurality of dispersion grooves formed from one ofan upper and a lower surface of the light guide plate.
 25. The method ofclaim 24, wherein each of the plurality of dispersion grooves isseparated from each other within the light path converter.
 26. Themethod of claim 24, wherein the dispersion grooves are formed along thetraveling direction of the lights incident on the light guide plate andthe number of the dispersion grooves is increased as the dispersiongrooves are spaced farther away from the light sources.
 27. The methodof claim 26, wherein the dispersion grooves form a fan shape of which awidth of the fan shape is increased as the dispersion grooves are spacedfarther away from the light sources.
 28. The method of claim 24, whereinthe dispersion grooves are formed in a hemispheric, semi-circular, orsemi-polygonal shape.
 29. The method of claim 20, wherein the light pathconverter comprises: a plurality of first dispersion grooves formed atan upper surface of the portion of the light guide plate; and aplurality of second dispersion grooves formed at a lower surface of theportion of the light guide plate.
 30. The method of claim 29, whereinthe first and second dispersion grooves face each other.
 31. The methodof claim 29, wherein the first dispersion grooves are formed between thesecond dispersion grooves.
 32. The method of claim 29, furthercomprising a light scattering part disposed in the dispersion groovesand including a scattering material.